1. Field of the Invention
The present invention relates to a phototaking system of a camera for silver salt film, a still video camera, a video camera or the like, and particularly to an optical apparatus provided with a driving unit for moving a lens unit for zooming or focusing or both in a portion of a lens barrel.
2. Related Background Art
It has heretofore been usual with the lens driving mechanism of a camera or the like to transmit the drive force of a motor by a driving mechanism such as a feed screw or a cam cylinder and a belt and a gear with the aid of a DC motor or a stepping motor to thereby move a focusing lens or a lens for zooming.
However, such example of the prior art has suffered from problems which will hereinafter be described.
Torque created by a DC motor or a stepping motor is generally a drive force in the direction of rotation, and to rectilinearly move a lens in the direction of the optic axis, members such as a feed screw and a cam have become separately necessary and it has been difficult to make a lens barrel compact.
Also, vibration and noise have been produced from the motor unit, and the gear unit and torque efficiency has been low, and this has given rise to a problem that much electric power is consumed.
On the other hand, the applicant has proposed in Japanese Laid-Open Patent Application No. 58-16208 a mechanism for rotating a lens holding cylinder helicoid-coupled to a body by the electromagnetic induction between the lens holding cylinder and the outer cylinder thereof to thereby move a lens unit back and forth, but loss of energy occurs in the helicoid-coupled portion and the movement still exists and the driving operation is performed in indirect manner.